The present invention pertains to pneumatic actuators. More particularly, but not by way of limitation, the present invention pertains to feedback control of on/off pneumatic actuators usable with a vitrectomy probe.
Microsurgical procedures frequently require precision cutting and/or removing various body tissues. For example, certain ophthalmic surgical procedures require cutting and removing portions of the vitreous humor, a transparent jelly-like material that fills the posterior segment of the eye. The vitreous humor, or vitreous, is composed of numerous microscopic fibrils that are often attached to the retina. Therefore, cutting and removing the vitreous must be done with great care to avoid traction on the retina, the separation of the retina from the choroid, a retinal tear, or, in the worst case, cutting and removal of the retina itself. In particular, delicate operations such as mobile tissue management (e.g. cutting and removal of vitreous near a detached portion of the retina or a retinal tear), vitreous base dissection, and cutting and removal of membranes are particularly difficult.
The use of microsurgical cutting probes in posterior segment ophthalmic surgery is well known. These cutting probes typically include a hollow outer cutting member, a hollow inner cutting member arranged coaxially with and movably disposed within the hollow outer cutting member, and a port extending radially through the outer cutting member near the distal end thereof. Vitreous humor and/or membranes are aspirated into the open port, and the inner member is actuated, closing the port. Upon the closing of the port, cutting surfaces on both the inner and outer cutting members cooperate to cut the vitreous and/or membranes, and the cut tissue is then aspirated away through the inner cutting member.
During surgical procedures, cutting rates and duty cycle are frequently controlled to regulate the amount of tissue that can be cut in a given time period. For example, when cutting in less sensitive areas, such as areas spaced from the retina, the cutting may be done in a manner that lends to efficiency. When cutting in more sensitive areas, such as those nearer to the retina, the cutting may be done in a careful manner, where the amount of tissue cut per cutting cycle is decreased. This is accomplished by controlling the duty cycle, or the percentage of time in a cutting cycle that a port is open. This is determined by dividing the amount of time the port is open by the total amount of time of a single cutting cycle. Larger duty cycles provide for efficient cutting while smaller duty cycles provide for slow and careful cutting.
Variations in characteristics of cutter components, including those from initial critical component tolerances, can introduce inconsistencies in duty cycles across cutters. To address this, current systems are calibrated at the time of manufacturing. This factory calibration can be a time consuming and costly activity. Further, it is done with the assumption that changes over time of these same critical components will not significantly affect performance. This assumption however, may not be valid in many cases. As components become worn over time, the precision and accuracy of controlled parameters may become adversely affected. These variations can potentially degrade the performance of the system or even prevent the system from reaching its desired operating targets, potentially resulting in a cutter that does not fully open or close. These performance degradations and failures become more pronounced and more frequent through continued use.
Despite the above described advances, a need still exists for improved vitrectomy probes. In particular, vitrectomy probes that compensate for discrepancies arising from initial tolerances or degradations of components over time.
The present disclosure is directed to addressing one or more of the deficiencies in the prior art.